The pipeline steel is usually produced by adding niobium and vanadium alloying elements.The titanium alloyed pipeline steel was studied in the paper to reduce the production cost and enhance the competitive ability of pipeline steel.The steel containing 0.070%Ti was refined in the laboratory vacuum refine furnace.The dynamic CCT curve of developed steel was conducted on Gleeble-1500 thermal simulator and multi-pass deformation tests of studied pipeline steel were performed to simulate the CSP hot-rolling technology.Corresponding microstructures were observed and the influences of such technology parameters as deformation strain,deformation temperature, cooling rate and finishing temperature etc.on microstructure were analyzed.The dynamic CCT curve was obtained.The test results showed that the volume fraction of acicular ferrite in the microstructure of Ti-microalloyed X70 pipeline steel increased obviously with the increase of cooling rate after thermo-mechanical deformation.However,the volume fraction of acicular ferrite varies scarcely after the cooling rate of 20℃/s.In order to obtain Ti-microalloyed X70 pipeline steel with excellent compound mechanical properties which has acicular ferrite as the main ideal microstructure,the cooling rate should be controlled to be 20℃/s or more.The higher of the finishing temperature,the more of the volume of acicular ferrite and the less of the volume of polygonal ferrite.The quite fine microstructure can be obtained by lowering the finish-cooling temperature.The results have shown that it is possible to produce the Ti-addition X70 pipeline steel from the point of view of microstructure.
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